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Repairing (Silver Brazing) Bandsaw Blade

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  • Repairing (Silver Brazing) Bandsaw Blade

    I wiped the teeth off of the plane carbon steel bandsaw blade that came with my 7x12 the other day. Had to use the little bandsaw (glad I kept it as a spare) for the last week. I ordered in a nice Lennox M42 bi-metal blade to try on the 7x12 and ... I managed to order the wrong size. Of course I didn't realize it until to late. It took a week to get here and the saw won't adjust out enough to fit it up. I've got a couple more blades coming that are the right size, but I really need my saw going.

    I decided to cut an inch out of the blade, but haven't done it yet. I got the geometry for cutting and silver soldering figured out I think. However I am confused about cooling the blade afterwards. Some guys use a wet rag and fast cool it. Others seem to indicate that you should slow cool it and anneal it. To the point that they play a flame over the area around the repair to slow the cooling.

    What have you done? How did it work out?

    No, I don't have a blade welder. LOL.

    I did stop by my local Praxair shop and pickup some Silvalloy 45%. Youch! That stuff costs almost as much as the blade. $22 for 30 grams. On the other hand it won't take much of it. Should last me the rest of my life.
    *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

  • #2
    You already know to grind the ends to a scarff joint and make up a little jig to hold the ends overlapped correctly and in alignment?

    The couple of times I've done blades for my wood cutting bandsaw I just let it cool naturally. Never had an issue at the joint. But those were not bimetal blades.
    Chilliwack BC, Canada

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    • #3
      I've always just let it cool on its own.
      ----------
      Try to make a living, not a killing. -- Utah Phillips
      Don't believe everything you know. -- Bumper sticker
      Everybody is ignorant, only on different subjects. -- Will Rogers
      There are lots of people who mistake their imagination for their memory. - Josh Billings
      Law of Logical Argument - Anything is possible if you don't know what you are talking about.
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      • #4
        The bimetal part is a thin strip of high speed steel induction welded to a carbon steel strip. The teeth are cut into the high speed steel so it doesn’t add much to blade strength.

        Comment


        • #5
          Bi-metal blades work because the teeth are not affected by the brazing process. Hi carbon blades will have the teeth adjacent to the joint softened but not completely soft as in annealed because the thin blade cools fast in air. They will, however, lose those teeth first as the blade is used. So, if you buy a bulk reel of blade, make sure it is bi-metal. Anything else is false economy.

          RWO

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          • #6
            Originally posted by BCRider View Post
            ... and make up a little jig to hold the ends overlapped correctly and in alignment?
            +1

            If not absolutely essential, a proper jig surely makes fixturing much more pleasant.

            No need to be fancy, even plywood works in a pinch with adequate air gap from flame/heat. If you decide you prefer making blades over buying them, put some time into making a nice jig.

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            • #7
              Yeah, the jig part is easy. I figured two pieces of angle clamped to a straight edge with a gap between them and then slapped in the vise would do. Back the blade up against the straight edge and clamp in proper overlap. Then remove straight edge and have full access for heating.

              I just wanted to make sure it was going to be worth the effort. Air cooling it is.


              Thanks guys.
              *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

              Comment


              • #8
                Originally posted by RWO View Post
                Bi-metal blades work because the teeth are not affected by the brazing process. Hi carbon blades will have the teeth adjacent to the joint softened but not completely soft as in annealed because the thin blade cools fast in air. They will, however, lose those teeth first as the blade is used. So, if you buy a bulk reel of blade, make sure it is bi-metal. Anything else is false economy.

                RWO
                Exactly what RWO said about the teeth near the joint. I have been doing the silver solder joint for years. Only need a scarf an 1/8 - 3/6 long. As for the adjacent teeth loosing their temper, has any one tried doing a quick quench on the tooth edges, maybe a air blast or a wet rag to the tooth edge of the blade?
                Joe B

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                • #9
                  Frank McLean recommended using a pair of slip joint pliers to clamp the joint while hot. This serves two purposes; it squeezes out excess solder from the joint and anneals it. I have been using this method with success for many years now. Scarf joint should be width of the blade.
                  Jim H.

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                  • #10
                    Originally posted by JCHannum View Post
                    Frank McLean recommended using a pair of slip joint pliers to clamp the joint while hot. This serves two purposes; it squeezes out excess solder from the joint and anneals it. I have been using this method with success for many years now. Scarf joint should be width of the blade.
                    I like the idea but one would have to work really fast or apply the pliers with one hand while keeping the joint hot enough to keep the solder liquid with the other.

                    I can't recall seeing it for years now but I made my own jig from a piece of roughly 1 1/4 angle about 4 or 5 inches long by milling a flat step along it and then cutting away a "U" about 1" wide for the joint to allow heating from both sides. Small model builder's C clamps held the blade ends to the angle. Worked like a treat but it's MIA from the last move 8 years ago.
                    Chilliwack BC, Canada

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                    • #11
                      Google Images: band saw blade brazing jig

                      Ken

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                      • #12
                        Originally posted by KMoffett View Post
                        Google Images: band saw blade brazing jig

                        Ken
                        No. You can't make me. LOL.

                        I finally got around to cutting an inch out of that blade and silver brazing it today. Just a few minutes ago. Of course the correct length new blades I ordered arrived yesterday. I'll probably take the brazed blade off and just keep it as a spare, but I had to put it on and slice a piece of steel with it to see if it would hold. The metal in this video is 1" (25.4mm) thick by about 3" (76.2mm) wide 4140HT. At the start of the video clip I had not yet opened up the air cylinder control valve to allow full speed. In fact I didn't realize it was open at all, and was surprised when I looked down and saw it was cutting. Never heard it start the cut.





                        Improvised Brazing Jig




                        Lined Up





                        Before Grinding


                        *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

                        Comment


                        • #13
                          Congratulations Bob!
                          Another feather to stick into your hat.
                          Always nice to pick up a new skill to help keep the wheels going forward next time that you're in a bind.

                          How did the teeth near the HAZ make out after the 4140 cut?
                          Home, down in the valley behind the Red Angus
                          Bad Decisions Make Good Stories​

                          Location: British Columbia

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                          • #14
                            There'll be no stopping you now.

                            Keep that first blade as a memento, but consider laying in a supply of blade stock w/ useful TPI's and widths. Some find it quite liberating knowing that they don't have to nurse an ailing blade, trying to coax it through a project late on a Saturday night.

                            Comment


                            • #15
                              Originally posted by EddyCurr View Post
                              There'll be no stopping you now.

                              Keep that first blade as a memento, but consider laying in a supply of blade stock w/ useful TPI's and widths. Some find it quite liberating knowing that they don't have to nurse an ailing blade, trying to coax it through a project late on a Saturday night.
                              Where do I find blade stock that isn't nearly the same price as blades?

                              I could use carbon steel for aluminum, but I prefer high speed M42. It just lasts longer for everything.
                              *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

                              Comment

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